There is provided an improved process for extracting hydrocarbons from a solid material and more particularly an improved process from extracting hydrocarbons from a diatomite ore by increasing the permeability of the diatomite ore to an extracting solvent.
Many earth formations contain deposits having substantial amounts of hydrocarbons. Included among these are oil bearing diatomaceous earths. It is known that a diatomaceous earth may act as a filter under the appropriate circumstances. However, where hydrocarbons are to be recovered by means of solvent extraction it is generally necessary to reduce the diatomite ore to fine particles in order to provide sufficient contact between the solvent and the hydrocarbons. Once the diatomite ore has been crushed it becomes sufficiently fine so as to prevent the passage of solvent therethrough if it remains in a stationary bed. Thus, a variety of processes have developed which use settlement techniques and a number of stages to bring the extracting solvent into contact with the diatomite ore and successively separate off the resulting oil-solvent mixtures.
A variety of extraction processes have been proposed for the removal of oil or other hydrocarbons from diatomaceous earths. For example, U.S. Pat. Nos. 4,239,617 and 4,167,470 issued to Karnofsky describe a process which attempts to recover petroleum crude oil from oil laden diatomite by a continuous stage wise countercurrent extraction-decantation process. Ore is extracted by countercurrent decantation with a hydrocarbon solvent. Solvent is recovered from the extract by multiple effect evaporation followed by stripping. The spent diatomite is contacted with water and solvent is recovered from the resulting aqueous slurry of spent diatomite by steam stripping at superatmospheric pressure.
As indicated in column two of each of those patents a heated slurry of diatomite and solvent is discharged into a settling zone where the particles of diatomite settle to the bottom as a thixotropic mud for removal through an underflow mechanism. Overflow from this first stage is then passed to a clarifier where fine solid material settles to the bottom. A series of extraction stages comprising mixers and thickeners is employed to further extract the oil and separate out any solid material including any fines.
J. H. Cottrell, "Development of an Anhydrous Process for Oil-Sand Extraction," published in M. A. Carrigy, ed., Athabasca Oil Sands: A Collection of Papers, Edmonton, Alberta: Research Council of Alberta, 1963 (hereinafter the Cottrell paper) discloses an anhydrous solvent extraction process using a three-stage drain circuit to extract hydrocarbons from water-wet Athabasca oil sands. Process conditions are controlled to ensure that the inner film of water coating the sand particles and surrounded by a bitumen film is maintained in order to enhance the free flow of hydrocarbons through an oil-sand bed. This was explained under the theory that the apparent diameters of the solid-water particles randomly laid-down in the draining step were quite uniform and were larger than those of most dry solids existing within a given oil-sand sample.
In a commercial plant proposed in the Cottrell article oil sand and hydrocarbon solvent would be mixed in a mixer and then passed as a slurry on a moving belt through three consecutive drains. A mixture of solvent and hydrocarbon would pass through the slurried bed in each drain under appropriate process conditions to maintain the water film. Solvent would subsequently be recovered from the spent slurry by steam stripping and from the raw bitumen product recovered from the first drain by fractionation.
These and other processes have suffered from one or more of several defects or limitations. For example, as evidenced by the foregoing processes there must generally be a relatively complex series of steps to separate off the solvent oil mixture from any spent diatomite ore. Similarly, a variety of equipment must often be employed to insure that the oil solvent mixture does not contain an excessive amount of fines. These and other limitations are substantially minimized if not eliminated by the present inventive method.